1. Field of the Invention
The present invention relates to an image forming apparatus, for example copiers, facsimile machines, printers and so on, in particular, to a sheet feeding apparatus capable of feeding a sheet without wrinkling thereof.
2. Description of the Related Art
In a conventional sheet feeding apparatus, wrinkling of to sheet, which generally occurs when to sheet is fed by a heating roller having a heater therein and a pressure roller in pressure contact with the heating roller, is a common problem. To solve such a problem, as illustrated in Japanese Patent application Laid Open No. 05-40428, a heating roller which is driven by a motor and has a larger diameter at both edge portions relative to a center portion, and a pressure roller which has a equal diameter along an axis thereof and is in pressure contact with the heating roller are used. In such a conventional sheet feeding apparatus, both side edge portions of the sheet are fed faster than the center portion due to a strong pressure applied to the sheet at the edges, and, accordingly, the sheet is expanded toward both edges from the center thereof, thereby avoiding some wrinkling thereof.
However, in the conventional sheet feeding apparatus, the pressure roller must be precisely manufactured with a clearance of only 1/100 mm to avoid the above described wrinkling of the sheet. As a result, a manufacturing cost thereof tends to be high.